Conventionally, majority of fish tank is designed to view aquarium fish, such as tropical fish, aquarium fish, or goldfish, from the side. Besides, a conventional fish tank for viewing fish from the top (Japan Utility Model Publication No. 1993 (Heisei 5)-91318) has a gap between the water surface and a top plate and, therefore, suffers from diffuse reflection resulting from, for example, waves on the water surface, making it impossible to view fish clearly. As a fish tank disclosed in Japan Patent Application No. 1992 (Heisei 4)-47528 has a convex table top plate, there exists a problem in practical use, such as high manufacturing cost. For viewing aquarium fish clearly from the fish-tank there are several problems as mentioned above so that a demand for improvement is required.